Image Version Checker

This is a little piece of CI tooling I wrote as a way to start learning Go. This could have easily been a python script and there is not much leverage of what makes Go great, it is pretty straight forward stuff. I just wanted a way to know if a docker image was updated to kick off a build elsewhere.

What it does

This will poll a repisitory on docker hub registry to pull latest manifest for a given tag and compare it against the last time it was ran, in essence if there is a change to the image. It will then send a workflow_dispatch event to a github repo. I currently capture that event and rebuild an image via github actions that is based off the image I am polling.

Usage

I think docker is probably the best way to implement this as I want to keep the process running indefinitely and docker these days is easier than to daemonize. You will need to create a digest file to mount, this will act as permanent store for the current digest of the image, that way it can persist reboots and whatnot.

touch /path/to/digest.out

Be careful about not using a suffix as docker seems to always want to mount things as dirs. Might clean that up at some point

docker pull ghcr.io/stshontikidis/image_check
docker run -d \
    -e GH_REF=master \
    -e GH_REPO=stshontikidis/nextcloud_preview \
    -e GH_TOKEN=<PAT for repo> \
    -e GH_WORKFLOW=5323441 \
    -e DOCKER_REPO=library/nextcloud \
    -e DOCKER_TAG=stable \
    --name image_check ghcr.io/stshontikidis/image_check

Or you better yet, you should probably be using compose

version: "3"

services:
  poller:
    image: ghcr.io/stshontikidis/image_check
    volumes:
      - /path/to/digest:/tmp/digest
    env_file:
      - .env

Environment Variables

Var	Description
DOCKER_REPO	The repo you want to poll on docker hub registry
DOCKER_TAG	The tag for image you are polling the status of
GH_REPO	The repo on github you want to send the workflow action to.
GH_REF	A The git reference for the workflow. The reference can be a branch or tag name.
GH_WORKFLOW	The ID or name of the workflow. You can find the ID using an API via curl.
GH_TOKEN	PAT with repo scope for given github repo.

Checking out the workflow_dispatch API might help clearify smoe of the envs.